1. Field of the Invention
The invention is in the field of nuclear waste control and is particularly directed toward the elimination of long-lived radioactive nuclides of nulcear reactor waste.
2. Description of the Prior Art
The difficulties encountered in attempting to safely dispose of radioactive wastes generated by the fission process in nuclear reactors is probably the largest single cause of public resistance to the construction of nuclear power stations. A decade ago it was liberally estimated that 200,000 megawatts of nuclear generated electricity would be available by 1980. Today this expectation is down by one half. A major argument against permitting the further spread of nuclear power involves concern over methods proposed for disposal of the nuclear waste products. Present methods of disposal of nuclear waste, which may be in the gaseous, liquid or solid state consist either of dilution and dispersion or storage. In the first approach radioactive gases or liquids are diluted with large volumes of air or water to reduce the activity per unit volume to an allegedly safe level and released into the environment. In the second use, radioactive materials are stored in the containers in the ground or under the sea. With adequate safeguards, storage for about 30 years suffices to remove the harm from relatively short-lived radioactive nuclides, but the situation is quite different for the long lived wastes. Fortunately, the majority of the fission wastes have half-lives less than one year, which means that at worst they must be stored for 33 years to be reduced to 10.sup.-10 of their original amount. However, eighteen fission waste products as well as all the actinide waste products have half-lives greater than one year, but less than 10.sup.10 years, and it is these products that pose the long term storage problem. To ensure that long lived waste products are kept out of the biosphere until they become harmless--involving periods of hundreds of thousands or millions of years--present proposals involve burial in geological salt formations or other formations such as granite, quartzite, tuff (welded volcanic ash) and shale.
The burial solution to the waste problem is based on the assumption that the geological formation will remain stable for the necessary containment period. While this assumption is reasonable for plutonium, for example, it is not evident for the longer lived wastes including the fission products Pd.sup.107, Tc.sup.99, I.sup.129, CS.sup.135, and Zr.sup.93, as well as the actinides.
In view of the extreme hazard that would be created if these materials were to be released into the biosphere, there is a strong and growing resistance to the "bury it and forget it" philosophy, and this opposition has now developed to the point of significantly slowing the growth of nuclear power. It is therefore most desirable if a method could be found to completely eliminate the noxious radioactive wastes from the environment.
Two methods have been suggested for such a final solution to the waste problem. Extraterrestrial disposal would permanently remove the wastes by transportation by rocket into the sun. Two major problems face this technique. First the cost, and second, but more significant, there is the possibility of vehicle failure within the atmosphere leading to a highly dangerous level of radioactive contamination.
A more attractive technique involves the direct transmutation of the dangerous waste materials by neutron bombardment into innocuous materials, or at worst short lived radioactive species. Such a transmutation can be achieved, for example, by recycling waste products back into the reactor which produced them. Such nuclear transformations have been discussed in the literature but have been found only applicable for effective elimination of the actinides produced by neutron capture, e.g., "Advanced Waste Management Studies Progress Report", 8, BNWL-B-223 (1973); H. C. Claiborne, "Neutron Induced Transmutation of High-Level Radioactive Wastes", ORNLTM-3964, 1, 24; and "High-Level Radioactive Waste Management Alternatives", 4, 9, BNWL 1900 (1974). The applicability of transmuting long-lived fission products as well as the actinides by neutron capture in reactors has not been regarded as practical since such a procedure reputedly produces more long term waste than it removes.